The invention resides in a circuit arrangement for analyzing a clocked signal reflected from an object, particularly an optical signal, including at least one radiation emitter which is connected to an oscillator for the delivery of the clocked signal, at least a radiation receiver which receives radiation pulses delivered by the radiation emitter and reflected from the object, and a comparator by means of which the output signal pulses of the radiation receiver are compared with reference signal pulses, wherein the amplitude of the reference signal pulses depends on the output signal of the comparator.
Such a circuit arrangement is known, for example, from DE 100 01 943 A1. In the known arrangement, a clocked optical signal sent out by a radiation emitter and reflected by an object is received by a radiation receiver. The radiation receiver further receives directly a blocked optical signal which is sent out by a second radiation emitter and which is phase-shifted relative to the optical radiation signal sent out by the first radiation emitter by 180°. This means that, whenever there is a gap between the signal sent out by the first radiation emitter and reflected from the object, the radiation receiver receives a radiation pulse of the second radiation emitter.
The signal development present at the output of the radiation receiver depends therefore on the height of the amplitude of the received signal. If the amplitude received by the radiation receiver of the signal of the first radiation emitter reflected by the object is as large as the amplitude of the signal of the second radiation emitter received by the radiation receiver, the radiation receiver delivers at its output a DC voltage.
If the distance of the object from the first radiation emitter or, respectively, the radiation receiver changes, also the amplitude of the signal of the first radiation emitter reflected from the object and received by the radiation receiver changes. As a result, a rectangular voltage is provided at the output of the radiation receiver. In a circuit arrangement connected to the radiation receiver, a control voltage is formed from this rectangular voltage by way of which the strength of pulses emitted from the second radiation emitter is set.
The circuit arrangement is so designed that the control value counteracts the difference between the amplitudes of the reflected signal and the reference signal. That is, the amplitude of the reference signal is adapted to the amplitude of the reflected signal so that the square voltage present at the output of the radiation receiver is almost zero.
In the known circuit arrangement, it is a disadvantage that a second radiation emitter is required and that the light emitted by the second radiation emitter becomes stronger when the reflection is improved, that is, when the reflected light received by the radiation receiver becomes stronger. As a result, the energy requirements are relatively high.
From U.S. Pat. No. 4,068,222 A, a circuit arrangement for the automatic level adjustment for optical sensors with pulsed radiation for example for surveillance apparatus is known in which, by means of changes in the radiation conditions between a pulsed IR emitter and an IR receiver whose clocked output amplitude is adjustable in accordance with emission pulses, alarm signals are generated and the adjustable receiver output signal voltage is compared with the reference signal voltage derived from the emitter in a comparator which is clocked by the pulse frequency of the emitter. After the comparator there is a control voltage generator with an integration stage for a control member which controls the output amplitude of the receiver, and an evaluation logic stage to which alarm generators and an adaptation indicator are connected.
It is the object of the invention to provide a circuit arrangement of the type as discussed initially but which has substantially reduced energy requirements.